I. Field of the Invention
The invention relates to butterfly fire dampers for use in air ducts.
II. Description of the Prior Art
Multiple, folding blade fire dampers having a plurality of blades disposed within a frame having an inwardly depending flange are known in the prior art, for example, my U.S. Pat. Nos. 3,814,165 and 3,866,657.
In my U.S. Pat. No. 3,899,156, a single blade fire damper is described along with some problems which accompany the use of the multiple, folding blade fire damper type.
When a fire occurs on one side of the damper, often the damper is equipped with means for automatically closing the blades and preventing spread of the fire to the other side of the damper. However, the heat from the fire on one side of the blade is often transmitted by the blades to heat the air on the other side.